Interrelation between nanostructure and optical properties of oxide thin films by spectroscopic ellipsometry

Nanostructured thin oxide films of SnO2, V2O5 and indium tin oxide (ITO) were deposited by conventional and plasma-assisted chemical vapor deposition (CVD, PECVD) on different substrates and at different temperatures. Optical properties of the films were determined by spectroscopic ellipsometry in the energy range 1.5–5.5 eV. A parameterized analysis, based on Lorentzian oscillators combined with the Drude model, along with Bruggeman effective-medium approximation (BEMA) modeling, was used to determine the optical constants of thin films independently from the reference dielectric functions of the bulk materials. In this way, correlation between the optical properties and nanostructure of thin films could be established. In particular, in order to discuss the dependence of optical constants on grain size, SnO2 nanostructured films have been considered, using a parameterization based on a double Lorentzian oscillator. Nanocrystalline V2O5 thin films have demonstrated the correlation between optical constants (described by four Lorentzian oscillators) and crystalline/amorphous volume fractions. Finally, ITO thin film optical properties are described by a combination of a double Lorentzian oscillator with the Drude model; by this analysis, gradients in the structural and optical properties of ITO are demonstrated.